Date Full Report Received05/30/2010
Date Abstract Report Received05/30/2010
Funded ByIowa Pork Producers Association
Porcine reproductive and respiratory syndrome virus (PRRSV) NC16845 was isolated from porcine tissue submitted to the Iowa State University Veterinary Diagnostic Laboratory in 2006. The isolate originated from twelve-week-old pigs from North Carolina exhibiting lethargy, coughing, respiratory distress and weight loss. The excessive mortality and morbidity was unusual and prompted further investigation of the PRRSV for unique genomic and growth characteristics. The objectives of this study were to (1) sequence the full genome of a recently isolated PRRSV designated NC16845 and (2) evaluate the in vitro growth characteristics compared to prototypes VR-2332 and MN184. Sequence analysis demonstrated that NC16845 was similar to atypical PRRSV JA142 although the NC16845 restriction fragment length polymorphism (RFLP) pattern is 1-18-2. One PRRSV sequence in the PRRSV database was found to be similar to NC16845 in the region of the attachment glycoprotein (ORF5) and was also isolated in North Carolina at approximately the same time. The NC16845 genome is 15,385 nucleotides in length, approximately 26 nucleotides shorter than the prototype VR-2332. Nucleotide degeneracy was noted in the replicase gene that corresponded to the highly variable non-structural protein 2 (nsp2) region similar to differences identified in the virulent strain PRRSV MN184. However, considerable nucleotide divergence was demonstrated between NC16845 and VR-2332 and MN184. NC16845 demonstrated slower replication characteristics in cell culture compared to VR-2332 and another virus isolated in the 1990’s, VR2385; however, replication kinetics were somewhat similar to MN184. Plaque sizes were smaller compared VR-2332 but larger than those of MN184. These results emphasize the inverse correlation between in vitro growth characteristics and the in vivo virulence where highly virulent PRRSV isolates are less adapted to cell culture and exhibit a slower rate of replication and growth. The results indicate unique genomic and growth features of the novel PRRSV isolate NC16845. Consistent with previously characterized virulent PRRSV isolates, NC16845 contains a shorter genome with variations in specific regions that are reflective of a slower growth rate in vitro. In addition, NC16845 demonstrated the unique ability of PRRSV to alter its genome and adapt to selection pressure resulting in PRRSV isolates that may be more virulent and capable of circumventing prior herd immunity.
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